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United States Patent |
5,209,825
|
Badat
,   et al.
|
May 11, 1993
|
Preparation of purified concentrated BDO
Abstract
A distillation process for the preparation of purified concentrated BDO.
High boiling impurities, including color formers, precursors of color
formers and tar formers are removed from the BDO early in the process and
under mild conditions.
Inventors:
|
Badat; Hashim M. (Houston, TX);
Gelblum; Peter G. (Philadelphia, PA);
Trotter; Robert E. (Hockessin, DE)
|
Assignee:
|
E. I. Du Pont de Nemours and Company (Wilmington, DE)
|
Appl. No.:
|
691155 |
Filed:
|
April 24, 1991 |
Current U.S. Class: |
203/29; 203/77; 203/80; 549/429; 568/868 |
Intern'l Class: |
B01D 003/10; B01D 003/14 |
Field of Search: |
203/29,14,18,50,77,80,DIG. 6
549/429
568/868
|
References Cited
U.S. Patent Documents
3891511 | Jun., 1975 | Danneil et al. | 203/84.
|
4175009 | Nov., 1979 | Copelin | 203/96.
|
4197248 | Apr., 1980 | Copelin et al. | 204/14.
|
4332645 | Jun., 1982 | Muller et al. | 203/14.
|
4348262 | Sep., 1982 | Stock et al. | 203/37.
|
4383895 | May., 1983 | Ernst et al. | 203/77.
|
4419189 | Dec., 1983 | Caracciolo | 203/77.
|
Primary Examiner: Manoharan; Virginia
Parent Case Text
This application if a continuation-in-part of application Ser. No.
07/252,967 filed Oct. 4, 1988, now abandoned.
Claims
We claim:
1. A process of purifying crude 1,4-butanediol to purified concentrated
1,4-butanediol, said crude butanediol containing about 1 to about 30% by
weight of water and organic impurities that boil lower than
1,4-butanediol, about 0.05 to about 5% by weight of high boiling organic
compounds and inorganic and organic salts, and about 70 to 99% by weight
of 1,4-butanediol, which consisting essentically of:
fractionating said crude butanediol feed stream at a temperature of no more
than 210.degree. C. into a purified concentrated 1,4-butanediol fraction
and a bottom fraction;
separating as bottoms a fraction having a weight of not greater than 6% of
the weight of said feed stream, said bottoms fraction containing high
boiling organic compounds, inorganic and organic salts and not more than
60% by weight of 1,4-butanediol, and
separating as overhead said purified concentrated 1,4-butanediol fraction
which contains about the same amount of water as, and less high boiling
organic compounds and inorganic and organic salts than, were in said crude
butanediol feed stream, the amount of said high boiling organic compounds
and said salts in said overhead fraction being not more than 0.1% by
weight, based on the total organics.
2. The process of claim 1 in which overhead fraction is further
fractionated to separate components having a boiling point lower than
1,4-butanediol.
3. The process of claim 2 in which the fraction remaining after separation
of components having a lower boiling point than 1,4-butanediol is further
fractionated so as to separate components having a higher boiling point
than said butanediol, thereby forming a refined and purified
1,4-butanediol consisting essentially of 99.9% 1,4-butanediol and 0.05%
high boiling compounds at a yield of at least 95% 1,4-butanediol, the APHA
color of a polyester made from said refined and purified 1,4-butanediol
being no greater than 15.
4. The process of claim 2 in which the fraction remaining after separation
of components having a lower boiling point than 1,4-butanediol is further
fractionated so as to separate components having a higher boiling point
than said butanediol, thereby providing purified refined 1,4-butanediol in
a yield of at least 90%.
5. The process of claim 4 wherein said yield is at least 95%.
6. The process of claim 4 wherein said bottoms fraction has a weight of not
greater than 3% of the weight of said feed stream and contains no more
than 40% by weight of 1,4-butanediol.
7. The process of claim 1 in which the overhead fraction is further
fractionated to separate components having a higher boiling point than
1,4-butanediol.
8. The process of claim 1 in which one of salts in the crude 1,4-butanediol
is sodium formate.
9. The process of claim 1 in which the crude BDO is obtained by the
buffered reaction of formaldehyde and acetylene to form butynediol,
following by hydrogenation of butynediol to form butanediol, and then
concentrating that product.
10. The process of claim 1 in which the fractionation is carried out at a
pressure in the range of about 40 to 80 torr.
11. The process of claim 1 wherein the water content in said crude
butanediol and in said purified concentrated 1,4-butanediol fraction
separated as overhead are both between about 1 and 15% by weight.
12. The process of claim 1 wherein the water content in said crude
butanediol and in said purified concentrated 1,4-butanediol fraction
separated as overhead are both between about 1 and 8% by weight.
13. The process of claim 1 wherein the water content in said crude
butanediol and in said purified concentrated 1,4-butanediol fraction
separated as overhead are both between about 4 and 6% by weight.
14. The process of claim 1 wherein a portion of said overhead fraction is
cyclized and distilled to form high purity non-color-forming
tetrahydrofuran in a yield of at least 94% based on said crude
1,4-butanediol.
15. The process of claim 14 in which the yield of tetrahydrofuran is at
least about 97% based on the 1,4-butanediol fed to the cyclization
reaction.
16. The process of claim 12 in which tetrahydrofuran is recovered by
azeotropic distillation.
17. The process of claim 1 wherein said bottoms fraction has a weight of
not greater than 3% of the weight of said feed stream and contains no more
than 40% by weight of 1,4-butanediol.
Description
FIELD OF INVENTION
The process of the invention relates to a method of purification of crude
1,4-butanediol by removing color formers and precursors of color forming
materials and precursors of tars by distillation. The color forming
materials, precursors of color forming materials and precursors of tars
are a portion of the high boiling organic compounds contained in the crude
1,4-butanediol. More specifically, the process of the invention relates to
a process for removing color formers and precursors of the color formers
and precursors of tar by first removing substantially all (99.9%) high
boiling organic compounds, and organic salts and inorganic salts from
crude 1,4-butanediol and subsequently removing water, low boiling
impurities and remaining high boilers.
1,4-butanediol is sometimes hereinafter referred to as BDO.
BACKGROUND
The preparation of butynediol by the reaction of formaldehyde and
acetylene, the subsequent hydrogenation of the butynediol to form crude
1,4-butanediol and the distillation of butanediol are described in U.S.
Pat. No. 4,371,723.
Preparation of "very pure" 1,4-butanediol by fractional distillation of a
water-free stream is described in U.S. Pat. No. 3,891,511.
When crude 1,4-butanediol is conventionally prepared from the starting
materials, formaldehyde and acetylene using buffered reaction conditions,
the resulting stream contains high boiling organic compounds, including
color forming materials, precursors of color and tar formers, inorganic
salts and organic salts including sodium formate that if not removed
eventually from the BDO, give a product that is not suitable for
high-volume, color sensitive end uses such as the formation of polyester,
polyurethane and in the preparation of tetrahydrofuran. These high boiling
compounds and salts, if not removed early in the purification process
react with themselves and with BDO which produces tars and color formers;
thus reducing the yield of BDO and reducing its utility. These wastes are
economically undesirable, and are pollutants that pose difficult disposal
problems.
Now it has been found that these impurities (high boilers including color
forming materials and their precursors and precursors of tar, organic and
inorganic salts) present in the crude BDO, can be removed very efficiently
at very high yield by subjecting the crude BDO to distillation under mild
conditions wherein the amount of these impurities is reduced to not more
than 0.1% by weight based on the total organics. The purified concentrated
BDO can be further distilled to remove water, low boilers and remaining
high boilers to provide a BDO product for use in the color sensitive end
uses, e.g., polyester, etc., or the purified concentrated BDO can be used
to form a high purity colorless tetrahydrofuran. It has also been found
that the yield from crude BDO to refined BDO and yield from crude BDO to
tetrahydrofuran is greatly increased and that the purity of the finished
product BDO and tetrahydrofuran is very high. An additional important
feature of this invention resides in the fact that wastes can be minimized
at the source.
SUMMARY OF THE INVENTION
The present invention is a process of refining crude BDO to a purified
concentrated BDO.
Crude BDO contains 1-30% by weight water and organic impurities that boil
lower than BDO, 0.05-5% by weight of high boiling organic compounds and
inorganic and organic salts and 70 to 99% by weight BDO. Among the organic
impurities are various undesirable color formers including those that are
apparent when the BDO is mixed with acids such as hydrochloric acid,
precursors of color formers and precursors of tar.
The process of this invention comprises, fractionation of the crude BDO
feed stream at a temperature of no more than 210.degree. C. and usually at
a pressure in the range of about 40 to 80 torr, and separating as bottoms
a fraction having a weight of not greater than 6% by weight of the feed
stream, said bottoms containing high boiling organic compounds, inorganic
and organic salts and not more than 60% by weight BDO.
Separating as lighter cut overhead a fraction containing substantially the
same water content as in the crude BDO (about 1 to 30% by weight water)
and no more than one-fifth the quantity of high boiling organic compounds
and salts that were in the crude BDO, and based on total organics taken
overhead not more than about 0.1% by weight high boiling organic compounds
and salts. In other embodiments, the crude BDO and the purified
concentrated 1,4-butanediol overhead fraction contained between about 1
and 15% by weight water, preferably between about 1 and 8% by weight water
and most preferably between 4 and 6% by weight water.
The lighter cut overhead fraction may be further fractionated to remove
components having a lower boiling point than BDO, such as water, low
boiling alcohols and aldehydes, followed by the subsequent removal of the
remaining quantities of 0.1% by weight high boilers and salts, or the high
boilers may be removed first and then the low boilers removed from the
lighter cut overhead fraction. The yield of purified refined
1,4-butanediol recovered at this point in the process will be at least 90%
by weight, based on the weight of the crude butanediol used as a starting
material in the process. Preferably, at this stage in the process, one
will have formed a refined and purified 1,4-butanediol consisting
essentially of 99.9% 1,4-butanediol and 0.05% high boiling compound. The
latter may form color-forming compounds in the refined and purified
1,4-butanediol, but the APHA color of the polyester made from the refined
and purified 1,4-butanediol will be no higher than 15. Moreover, in a
preferred embodiment, the yield will be at least 95%.
Furthermore, all or a portion of the overhead stream may be directly used
to make tetrahydrofuran by cyclization in an acidic reaction, yielding a
high grade tetrahydrofuran at a high yield, e.g. about 94 to about 97%
based on BDO in the overhead stream. The waste from this reaction is free
flowing and clear. The free-flowing waste is soluble in water and in
C.sub.1 to C.sub.4 alkanols.
The process of the present invention is particularly useful to purify a BDO
stream made by the buffered reaction of formaldehyde and acetylene,
followed by hydrogenation of the resulting butylenediol to form crude
1,4-butanediol. Such a crude stream contains a high boiling component,
various organic and inorganic salts including alkali salts of formic acid,
e.g. sodium formate, which if not removed early in the purification
process react with other components in the mixture to form color-forming
compounds.
BRIEF DESCRIPTION OF THE DRAWING
The figure is a flow sheet of the process of the present invention.
DETAILED DESCRIPTION
Referring now to the figure, a crude BDO feed stream 6, containing 1-30% by
weight water and organic impurities that boil lower than BDO, 0.05-5% by
weight of high boiling organic compounds and inorganic and organic salts
and 70 to 99% by weight BDO is fed to distillation column 1, which is
operated under mild conditions, for example, at pressure in the range of
about 40 to 80 torr and at a temperature of no more than about 210.degree.
C., more preferably at 45 to 50 torr, and 175.degree. to 185.degree. C.
Pressure of less than 40 torr may be employed ---- temperature is a more
significant factor than pressure in defining mild conditions.
The term "high boiling organic compounds" means compounds having a relative
volatility of 0.7 and less where BDO has a volatility of 1.
From distillation column 1, stream 7 is separated and fed to the thin film
evaporator 2, or similar low residence time, high mixing shear device for
further fractionation. Stream 7, contains high boiling organic compounds,
salts, and BDO.
From thin film evaporator 2, stream 8 is separated as residue. This stream
contains not more than 6% by weight of stream 6 and contains high boiling
organic compounds, salts and BDO. Stream 8 contains not more than 60% by
weight BDO. Stream 8 has a honey-like consistency at room temperature and
flows like water at 100.degree. C.; moreover, it is soluble in C.sub.1
-C.sub.4 alkanols and mixtures of water and one or more of said alkanols.
Stream 9 from thin film evaporator 2 is returned to the distillation
column 1 where it is again subjected to fractionation. Alternatively
column 1 could be modified so as to include the functional features of a
thin film evaporator, or just have more distillation plates, in which
case, the stream 7 may be treated directly as residue without recovery of
BDO.
The overhead stream 10 from column 1, which contains less than 0.1% by
weight high boiling organic compounds, salts, mostly BDO, water and a
small fraction of low boiling alcohols is split. A portion of the stream
is sent back to column 1 as reflux 11 to aid in purifying the vapors
coming up through column 1. The amount of stream that is refluxed will
usually range from about 2% to 20% by weight of stream 10. All or a
portion of the remaining portion of stream 10 may be used to form high
purity tetrahydrofuran by sending it through stream 12 to reactor 5 where
it is reacted under acid conditions at low pH and cyclized to form high
purity tetrahydrofuran at high yield. The tetrahydrofuran may be separated
from the water by azeotropic distillation apparatus 18. All or a portion
of remaining stream 10 (labeled 12a) may be treated in subsequent
distillation columns 3 and 4. The bottom stream leaving cyclizaton reactor
5 contains no more than 1% by weight of the feed purified concentrated
1,4-butanediol; that stream is free-flowing at below 100.degree. C., and
it is soluble in C.sub.1 and C.sub.4 alkanols and in mixtures of such
alkanols with water.
In the figure, stream 12a is first fractionated to remove water and low
boilers as overhead 13, resulting in a bottom stream 14 that contains BDO,
and very small amount of high boiling organic compounds on the order of
0.1% by weight or less, based on total organics. The stream 14 is then
subjected to further fractionation in column 4 where a further amount of
this high boiling organic fraction is removed in bottom stream 16. Stream
16 is returned to the distillation column 1 where it is again subjected to
fractionation. Stream 16 from the bottom of the distillation column 4
containing not more than 5% by weight of stream 14.
Very small overhead stream 15 is separated from the distillation column 4.
Stream 15 is mostly water. Very high purity BDO is removed as a side draw
stream 17 from the distillation column 4.
Alternatively stream 12a may be first subjected to distillation to further
remove high boiling organic compounds and salts and then subjected to
fractional distillation to remove water and low boilers.
EXAMPLE 1
In a three column embodiment of the process of invention crude BDO
containing:
______________________________________
BDO = 90.8%
Water = 6.07%
Low-boiling impurities
= 0.4%
Close-boiling impurities
= 0.6%
High-boiling impurities
= 2.13%
(including salts)
(Close-boiling impurities are compounds
with relative volatility of about 0.8 to
about 0.9, whereas High-boiling organic
impurities are compounds with a relative
volatility of 0.7 and less - where BDO
has a volatility of 1.)
______________________________________
is fed at the mid point or lower of the first column. In the embodiment
conventional packing or trays can be employed. In a preferred embodiment a
mixture of trays and packing is used in the first column and packing is
used in the second and third columns. In the embodiment it is sometimes
desirable to have at least five theoretical trays below the feed point.
High boiling organic compounds and salts are removed from the bottom of the
first column and fractionated in a low residence, high mixing shear
device, e.g. thin film evaporator, removing 3% of the column feed stream
containing concentrated high boiling organic compounds and salts
comprising 40% BDO. The first column and thin film evaporator are operated
at 45 torr pressure and 168.degree. C. temperature and at 80 torr pressure
and 185.degree. C. temperature respectively.
The overhead product obtained from the first column has following
composition:
______________________________________
BDO = 92.63%
Water = 6.27%
Low-boiling Impurities
= 0.41%
Close-boiling Impurities
= 0.61%
High-boiling Impurities
= 0.08%
______________________________________
The overhead product from the first column is used in preparation of the
colorless tetrahydrofuran and/or further distilled in the second and third
column to obtain very high purity BDO free from color-forming impurities.
The overhead product from the first column is fed to the second column at
the mid point or lower but usually not below the packing i.e. at least
five theoretical trays above the bottom. Low boilers and water are removed
at the top, and bottom product containing high boilers and BDO is fed to
the third column at the mid point. The second and third columns are
operated at the pressure of 50 torr and bottom temperature of 165.degree.
C.
High boilers are removed in the bottom purge from the third column and
recycled to the first column. A liquid stream, in a high yield of about 95
percent, contains BDO substantially free from high boiling organic
compounds, salts, and color forming material is removed at point below the
top packed section i.e. at least two theoretical trays below the top;
The product obtained as side draw has the following composition:
______________________________________
BDO yield = >95%
Color (APHA) = 0
Polyester color = 15
C O number = 0.013
Purity = 99.911%
Water = 0.007%
Low-boiling impurities
= 0.018%
Close-boiling impurities
= 0.028%
High-boiling impurities
= 0.036%
______________________________________
The color formers and precursors of color formers and precursors of tar
removed by the process of the invention are compounds that color the
polyester products made from the reaction of BDO and dibasic acid. The
color forming property is measured by first preparing a polyester with BDO
and then following test procedure described as ASTM D-1209 to measure the
color.
A portion of the BDO from the first column overhead is reacted in a
continuous stirred reactor under acidic conditions at low pH and cyclized
to form water and high purity tetrahydrofuran at at least 97% BDO to
tetrahydrofuran yield.
The overhead product obtained from the reactor has following composition:
______________________________________
Water = 25%
Tetrahydrofuran = 75%
______________________________________
A purge stream is separated from the bottom of the tetrahydrofuran reactor
containing not more than 1% by weight of reactor feed containing unreacted
BDO, organic tars, salts, high boilers and acid. The purge stream contains
not more than 65% by weight BDO.
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